1. Field of the Invention
This invention relates generally to a product illumination device for examination of passing product wherein multiple wavelengths and intensities may be selected, and particularly for use in for product sorting where two or more wavelengths are to be detected by a single photodetector.
2. Description of the Related Art
A typical sorting machine of the type with which the present invention is used is a high-speed sorting machine for use with small products, including fungible products in the food and pharmaceutical industries. As used herein, product refers not only to a manufactured good but also to component items from which production of a good may be accomplished. As a result, the invention may also be used in conveyor sorting machines, for sorting of other flowing materials, such as plastic pellets and ammunition, and for quality control examination of product.
For example, individual rice grains may be sorted in a gravity-fed sorter to separate grains selected as “substandard.” In the art, “substandard” may apply to a grain having any undesirable characteristic, including reflected wavelength (color), shape, size or breakage, or any other characteristic not within the limits for acceptable products for a particular sorting. Alternative feed systems, such as belt driven conveyors, are also well-known in the art. Alternatively, certain rarer products may be desirable and therefore deflected from the flow of the less rare and less desirable remaining products. Likewise other materials may be sorted from the product flow, including, such as in the case of harvested goods, non-product materials such as glass, rocks, sticks and bran.
Sorting machines may employ one or more optical sensors to differentiate based on reflected wavelength, size, moisture content or other characteristics as determined in radiation bands, which may be within or outside the visible light spectrum. When such sorting is accomplished by use of two radiation bands, the sorting procedure is referred to as bichromatic sorting. In bi-chromatic sorters, a combination of filters, typically red/green and red/blue, has been required to limit the wavelengths and/or intensity impinging on the product. Such a system requires significant disassembly, and therefore lost productivity, when any change to the wavelengths and/or intensity is desired. Such a change may be desired if a different product is to be sorted or if a different characteristic is selected for sorting.
Optical sorting machines of the type employ optical sensors that include multiple photodetectors, such as a charged-couple device and photodiode arrays. The photodetectors are positioned to observe the illuminated product stream through a light-penetrating window. The product stream typically passes between an optical sensor and a background, where the background matches the product stream in standard reflected wavelength so that only a variation in a product's reflected wavelength causes a detection event. The illumination is from one or more light sources directed at the product stream to cause standard reflectivity or transmission (transluminence) from standard products in the radiation bands being observed and to cause nonstandard reflectivity from nonstandard products in those bands.
One of the main components of such a sorting system is the illumination assembly. The illumination assembly provides a starting point for the reception quality of the vision system. Typically, the assembly is required to supply a uniform light supply and have a high intensity at the object point (sometimes referred to as the scanline) of the vision system. Most inspection systems include some sort of illuminator. Conventional illuminators include incandescent and fluorescent lamps and light emitting diodes. Various optical arrangements have been designed for better illumination, such as ringed lamp arrays, focused filament projectors, and fiber optic emitters. These include attempts to avoid uneven illumination which may result in detection of shadows as defects.
These prior art illumination sources present certain difficulties. To adjust the wavelength or wavelengths of light and the light intensity impinging on passing product, prior art teaches the use of filters, typically mounted adjacent the camera. The prior art is prone to waste energy as heat, rather than light, which must then be removed from the sorting machine. Moreover, the combining color band in a monochromatic application is limited.
Such sorting machines also include one or more ejector mechanisms located downstream of the sensor or sensors with multiple nozzles associated with one or more valves actuated by an electrical signal coordinated with sensor detection. When a product having or lacking selected criteria is detected, an electrical signal is produced to actuate the valve of the ejector nozzle associated with the predicted location of the selected product at the predicted time the selected product will pass the ejector. The time elapsed between the selected product passing the sensor or sensors and the selected product being ejected is minimal to limit possible vertical and/or horizontal deflection of the selected product upon contact with non-selected products. Each ejector is therefore normally located as close as possible to the plane at which the optical sensor or sensors reviews the passing products, typically referred to as the scanline, ideally being just downstream therefrom and closely adjacent thereto.
It is desirable is such sorting machines to provide for product examination under multiple wavelengths because product displays varying reflection factors at particular wavelengths. For example, it is advantageous to provide examination in the infrared region because the relative absorption and reflectance throughout the infrared spectrum is dependent upon the chemical composition and physical characteristics of the sample. Infrared illumination therefore provides additional data which may be used for sorting. Thus two or more different wavelengths may be utilized to produce data regarding two or more different characteristics. Detection of multiple infrared wavelenths permits the use of comparison algorithms that would otherwise not be available with data for a single wavelength.
Problematically, use of more than one wavelength for detection has presented various difficulties. A single photodetector is unable to simultaneously detect multiple wavelengths, therefore, the prior art attempted use of multiple photodetectors. Use of multiple photodetectors for multiple wavelengths, however, presents its own difficulties. Given the close proximity of the product, the illumination source and the photodetectors in the sorting machine, space is at a premium and presents difficulties in providing space to position and direct a photodetector for each wavelength to a single scanline on a common or near common plane. Moreover, it is difficult to align multiple photodetectors to a common scanline and to maintain that alignment over time. Finally, photodetectors are costly, thus the use of multiple photodetectors is a disincentive to the use of multiple wavelengths.
Depending on the product to be sorted and the characteristic or characteristics selected as the basis for sorting, a particular wavelength, or wavelengths, and intensity, or intensities, of light may be desirable for characteristic identification. In convention product sorting machines, such a change may require replacement of the existing illumination assembly, thereby requiring the sorting machine to be removed from service until filters or light sources are altered or exchanged.
It would be an improvement over the prior art to provide an illumination device that provides intense, consistent illumination of the products to be viewed along a linear or elongated scan line, thereby providing consistent identification of selected characteristics and substantially reducing mischaracterization of products as having occlusions or other defects actually caused by shadows.
Additionally, it would be an improvement to the prior art to provide an illumination device that may instantaneously adjust the wavelength or wavelengths and/or wavelength intensity impinging on passing product.
It would be a further improvement to the prior art to provide an illumination device that may be used to detect multiple wavelengths by a single photodetector.
It would be a further improvement to the prior art to provide an illumination device that reduces the need to remove a sorting machine from service to alter the wavelengths used for sorting.